Sorry I can't provide any real insight there - I haven't spent much time with Grudem's systematic theology for some time. One of the things I like about Horton's approach is how he positions theology in the context of a drama, a story

"The Christian faith is, first and foremost, an unfolding drama. Geerhardus Vos observed, “The Bible is not a dogmatic handbook but a historical book full of dramatic interest.” This story that runs from Genesis to Revelation, centering on Christ, not only richly informs our mind; it captivates the heart and the imagination, animating and motivating our action in the world. When history seems to come to a standstill in sin, guilt, and death, the prophets direct God’s people to God’s fulfillment of his promise in a new covenant.

B. DOCTRINE: THE GRAMMAR OF FAITH

The great doctrines of the Christian faith arise out of this dramatic plot. “And the Word became flesh and dwelt among us, and we have seen his glory, glory as of the only Son from the Father, full of grace and truth” (Jn 1:14). Where the world’s religions focus on timelessly eternal truths, the most important teachings of Christianity concern historical events"

Michael Horton, The Christian Faith: A Systematic Theology for Pilgrims on the Way (Grand Rapids, MI: Zondervan, 2011), 19–20.

Horton's book was the principle textbook for a series of systematic theology classes I took a while back. I found it very helpful. As has been mentioned, it does a good job of explaining theology in the context of the dramatic story of God's creative and redemptive relationship with humanity.

Sorry I can't provide any real insight there - I haven't spent much time with Grudem's systematic theology for some time. One of the things I like about Horton's approach is how he positions theology in the context of a drama, a story

"The Christian faith is, first and foremost, an unfolding drama. Geerhardus Vos observed, “The Bible is not a dogmatic handbook but a historical book full of dramatic interest.” This story that runs from Genesis to Revelation, centering on Christ, not only richly informs our mind; it captivates the heart and the imagination, animating and motivating our action in the world. When history seems to come to a standstill in sin, guilt, and death, the prophets direct God’s people to God’s fulfillment of his promise in a new covenant.

B. DOCTRINE: THE GRAMMAR OF FAITH

The great doctrines of the Christian faith arise out of this dramatic plot. “And the Word became flesh and dwelt among us, and we have seen his glory, glory as of the only Son from the Father, full of grace and truth” (Jn 1:14). Where the world’s religions focus on timelessly eternal truths, the most important teachings of Christianity concern historical events"

Michael Horton, The Christian Faith: A Systematic Theology for Pilgrims on the Way (Grand Rapids, MI: Zondervan, 2011), 19–20.

now this is very interesting, I have not thought about this approach before but it is a rather compelling argument

Doing a brief flyover on Bird (I couldn't resist) I will say this, I think given the proposition to choose I would go with Horton as you have done. Erickson and Grudem are better on the subject. I'm a sucker for a deal on this subject though so I will keep my purchase as I may hew some gems from Bird's labor.

Meanwhile, Jesus kept on growing wiser and more mature, and in favor with God and his fellow man.

I own Grudem and I find he's really down to earth on stuff so you can apply it without having to grind it down.

There are three volumes currently on my wish list that fit the sale. I'm trying to decide which ones to add. There's Millard, Joel Beeke's work,and Integrative Theology I'm kind of stuck in the valley of decision.

The mind of man is the mill of God, not to grind chaff, but wheat. Thomas Manton | Study hard, for the well is deep, and our brains are shallow. Richard Baxter

Of those two, definitely Bird. I own both, but Horton did not really speak to me. I like Bird's writing style which aims to tke the dry and dusty out of systematic theology (actually the promo video for the book was cool enough to sell it to me back then) - but still he is a first-rate theologian, not dumbing it down. His theological convictions are not bound to the sometimes weird boundary lines of US-american theological camps, which makes it a refreshing read for international evangelicals.